On wrapping machines, particularly for wrapping stacks of sweets and similar, in which the ends of tubular wrappings are closed using the known method described above, the scissor-type parting device is opened by means of a cam device, which moves the movable arms into the open position at a given point along the insertion stroke inside the relative end portion of the tubular wrapping for closing, and closes the movable arms at a corresponding point along the extraction stroke (the opening and closing movements, being governed as they are by the same cam device, necessarily being specular).
The above known method involves several drawbacks, mainly on account of the above movements imparted to the arms of the parting device.
In the first place, the parting device necessarily opens, during the insertion stroke, before reaching the end of the end portion to be deformed (otherwise, since the opening and closing movements are specular, the parting device would close at the same point at which it is opened, without effecting any deformation), and then proceeds in the open position until it contacts the relative end of the product, thus resulting in “crumpling” of the end portion.
In the second place, the parting device closes before it is fully withdrawn from the end portion being deformed, thus failing to ensure the opposite flaps of the end portion are properly taut when gripped between the folding-sealing members.
And finally, since the parting device closes before being fully withdrawn from the end portion, correct duckbill shaping of the outer portion of the end portion is not necessarily guaranteed.